A topographic map differs from other maps because it describes the surface features of the Earth. It uses special lines, called contour lines, to depict surface features. A topographic map has two parts. The map face provides a two-dimensional representation of the Earth's surface. The map margin surrounds the map face and provides information on interpreting the map face. Although the layout of topographic maps is similar between different maps, the specific information contained in the margins and on the map face are unique to each particular map.
Instructions
Margin Information
1. Locate the margin along the edge of the map face. Information is presented in the margin to facilitate the use of the map.
2. Find the margin at the top of the map. The title of the map is located on the right side of the top margin, and the author or agency that created the map is located on the left side of the top margin.
3. Locate the margin at the bottom of the map. Map production information is located on the left side of the bottom margin. Adjoining the map production information is the declination diagram. The declination diagram is a display of three arrows: one indicating true north, another indicating grid north and a third indicating magnetic north. The angle between these arrows is also displayed. The declination diagram allows the user to determine the correction between north on the map and north on a compass. Note that magnetic north varies each year, and the declination diagram is accurate for the year the map was made. For out of date maps, consult NOAA's National Geophysical Data Center in the resources for current information.
4. Find the scale at the center of the bottom margin. A fractional scale and a bar scale are posted here to aid in determining the real-world distances represented on the map. With the scale the contour interval of the map is given, which indicates the change in elevation between intermediate contour lines (light brown lines on the map face).
5. Locate the quadrangle location and road-classification key on the bottom right margin. The quadrangle location is useful in finding adjoining maps. The road-classification key shows how different types of roads are displayed on the map face. The date of the map is also located here.
6. Find the map numbers printed along the edge of the map face on the margin. These numbers indicate different coordinate systems, such as latitude and longitude, section, township, range numbers and UTM coordinate values. The names of adjoining quadrangles can be found in the corners around the map face.
The Map Face
7. Learn to identify common map symbols on the map face. These include the use of blue to indicate bodies of water, brown lines to indicate contour lines, and black boxes to represent buildings. A more detailed list of common topographic map symbols is available from the U.S. Geological Service.
8. Find the contour lines on the map. These brown lines represent an elevation for all points on that line. There are three types of contour lines displayed on the map: dark brown lines represent index contour lines, light brown lines represent intermediate contour lines, and dashed brown lines indicate supplementary contour lines. Index contour lines are numbered with the elevation of the line. Intermediate contour lines are spaced at equal increments of elevation between index contour lines. Supplementary contour lines (not always present) are located at an elevation halfway between the elevation of two adjoining intermediate contour lines.
9. Identify terrain features on the map by the location of contour lines in context to each other. Contour lines placed close together indicate steep slopes, while contour lines spaced farther apart represent gentle slopes. Closed circles of contour lines show hills. Contour lines in the shape of a "V" indicate a valley with the point of the "V" pointing up the valley. Contour lines in the shape of a "U" represent a ridge where the bottom of the "U" is pointing downhill.
10. Determine the direction of a slope by determining the contour line with the lower elevation. Draw an arrow to the higher contour line and this will indicate the direction, also known as aspect.
11. Calculate the slope of the ground by measuring the distance an elevation changes over a given distance. To determine this, measure the elevation change using the contour lines. Then use the map scale to determine the distance of the elevation change. Divide the change in elevation by the distance to estimate the slope.
Tags: contour lines, brown lines, declination diagram, brown lines represent, contour lines, lines represent